For successful magnetic recording, particularly at high densities, such as is currently employed in high density disc drive storage apparatus, there should be a predictable constant space in between a record medium and a transducer which is used to access the record medium for a wide range of operating parameters. Such spacing has a substantial effect, particularly at high densities on fringing flux patterns such that the resolution of the sensing and recording on a record medium is significantly affected. Unfortunately, the interaction of many parameters, especially with the thin, closely spaced discs, which are in use today, have a substantial effect on the predictability and maintainability on such desired constant spacing. Such parameters include the relative speed between the record medium and the transducer, and the interior of the surface areas surrounding the transducer, and disc storage substrate parameters, such as flexibility and thickness. In addition, given the very tight spacing margins in present use between a transducer and the medium, even temperature and humidity can have a significant effect on variations in medium to transducer spacing.
Prior attempts to solve this problem have been both complex, expensive, and space-consuming. For example, in U.S. Pat. No. 3,178,719, a flexible magnetic disc is mounted in close proximity to a flat air bearing surface of an annular plate referred to as a Bernoulli plate and is rotated at a relatively fast speed causing the disc to assume a stable position. A number of magnetic heads are included in the plate, and a partial vacuum forms around small areas of the disc around the magnetic heads by a vacuum pump which is included. Obviously, this is a complex and expensive approach. A simpler apparatus includes a Bernoulli plate with a groove which is open to the disk and is readily disposed along the disc; convex surfaces are located on either side of a head, generating a pull-down force on the disc in the region near the groove. Once again, this is an expensive approach requiring considerable investment in additional parts.
A more recent approach in U.S. Pat. No. 4,578,727 describes a contact type recording apparatus in which a flat air bearing surface surrounds an elongate opening to a negative pressure cavity with the record and playback head arranged in the cavity. The use of the cavity will help to stabilize the disc surface at least when it is immediately adjacent to the transducer which is to access the data on the disc. As with the other approaches, this one consumes valuable vertical space.
Thus the problem of eliminating flow instability in a high speed rotating disc continues to need a solution.